Smoking is the leading cause of preventable morbidity and mortality in the US. While approximately 70% of smokers attempt to quit each year, only 5-15% maintain abstinence for 12 months, even with effective pharmacological and psychological interventions. Novel therapies are needed for smoking cessation and relapse prevention. Previous studies show that early post-cessation craving or urge to smoke is a powerful predictor of relapse. A current model of the pathogenesis of addiction maintains that a substance of abuse causes a marked increase release in phasic dopamine release, which in turn strengthens or increases the salience of the memory of the drug experience, leading to a powerful and persistent memory that is easily activated, leading to drug craving and often to drug use. This highly salient memory is also implicated in the physiological arousal associated with craving responses to smoking cues. This process is thought to be implicated in relapse to drug use after even long periods of abstinence. Recent animal research indicates that retrieval returns a consolidated memory such as those associated with drug craving, to a labile state from which it must be restabilized to persist in a process termed reconsolidation. If memories of drug-related experiences are labile when reactivated, this could represent a window of opportunity in which the memory of drug use that underlies drug craving can be influenced pharmacologically. Our hypothesis is that post-reactivation administration of the B-adrenergic blocker, propranolol, following retrieval of drug-associated memories will reduce the strength or salience of the memory by influencing reconsolidation, a process called memory reconsolidation blockade. In this study we will test the hypothesis that a single dose of propranolol given one hour prior to smoking-related cue exposure (post-reactivation treatment) will decrease psychophysiological responses to smoking cues one week later and will predict clinical response to an ensuing series of 6 post-reactivation treatments with script-driven imagery and propranolol. In order to do so, we propose to conduct a randomized, double-blind, placebo-controlled trial of post-reactivation treatment with propranolol in 50 adult smokers. Outcome measures will include physiological responses to smoking-related cues after one and six post-reactivation treatments and smoking behavior during the treatment and during a 3- month follow-up period.